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Background— Although statins are reported to have a cardioprotective effect, their immediate direct influence on ischemia-reperfusion injury and the underlying mechanisms remain obscure. We investigated these issues an in vivo canine model. Methods and Results— Dogs were subjected to coronary occlusion (90 minutes) and reperfusion (6 hours) immediately after injection of pravastatin (0.2, 2, or 10 mg/kg), pitavastatin (0.01, 0.1, or 0.5 mg/kg), or cerivastatin (0.5, 5, or 50 μg/kg). Then myocardial phosphatidylinositol 3-kinase (PI3-K) and 5′-nucleotidase activities were measured, as well as infarct size. After 15 minutes of reperfusion, pravastatin caused dose-dependent activation of Akt and ecto-5′-nucleotidase in the ischemic zone, and the effect was significant at higher doses. Pitavastatin also significantly increased these activities, and its optimal dose was within the clinical range, whereas cerivastatin caused activation at the lowest dose tested. In all cases, both Akt and ecto-5′-nucleotidase showed activation in parallel, and this activation was completely abolished by wortmannin, a PI3-K inhibitor. The magnitude of the infarct-limiting effect paralleled the increase in Akt and ecto-5′-nucleotidase activity and was blunted by administration of wortmannin, α,β-methyleneadenosine-5′-diphosphate, or 8-sulfophenyltheophylline during reperfusion. Both collateral flow and the area at risk were comparable for all groups. Conclusions— Activation of ecto-5′-nucleotidase after ischemia by PI3-K activation may be crucial for immediate infarct-size limitation by statins. There seems to be an optimal dose for each statin that is independent of its clinical cholesterol-lowering effect.

Background— The blockade of β-adrenergic receptors reduces both mortality and morbidity in patients with chronic heart failure, but the cellular mechanism remains unclear. Celiprolol, a selective β 1 -blocker, was reported to stimulate the expression of endothelial NO synthase (eNOS) in the heart, and NO levels have been demonstrated to be related to myocardial hypertrophy and heart failure. Thus, we aimed to clarify whether celiprolol attenuates both myocardial hypertrophy and heart failure via the NO-signal pathway. Methods and Results— In rat neonatal cardiac myocytes, celiprolol inhibited protein synthesis stimulated by either isoproterenol or phenylephrine, which was partially suppressed by N G -nitro- l -arginine methyl ester (L-NAME). Four weeks after transverse aortic constriction (TAC) in C57BL/6 male mice, the ratio of heart weight to body weight (mg/g) (8.70±0.42 in TAC, 6.61±0.44 with celiprolol 100 mg · kg −1 · d −1 PO, P −1 · d −1 PO, P Conclusions— These findings indicated that celiprolol attenuates cardiac myocyte hypertrophy both in vitro and in vivo and halts the process leading from hypertrophy to heart failure. These effects are mediated by a selective β 1 -adrenergic receptor blockade and NO-dependent pathway.

Background— We and others have reported that transient accumulation of cyclic AMP (cAMP) in the myocardium during ischemic preconditioning (IP) limits infarct size independent of protein kinase C (PKC). Accumulation of cAMP activates protein kinase A (PKA), which has been demonstrated to cause reversible inhibition of RhoA and Rho-kinase. We investigated the involvement of PKA and Rho-kinase in the infarct limitation by IP. Methods and Results— Dogs were subjected to 90-minute ischemia and 6-hour reperfusion. We examined the effect on Rho-kinase activity during sustained ischemia and infarct size of (1) preischemic transient coronary occlusion (IP), (2) preischemic activation of PKA/PKC, (3) inhibition of PKA/PKC during IP, and (4) inhibition of Rho-kinase or actin cytoskeletal deactivation during myocardial ischemia. Either IP or dibutyryl-cAMP treatment activated PKA, which was dose-dependently inhibited by 2 PKA inhibitors (H89 and Rp-cAMP). IP and preischemic PKA activation substantially reduced infarct size, which was blunted by preischemic PKA inhibition. IP and preischemic PKA activation, but not PKC activation, caused a substantial decrease of Rho-kinase activation during sustained ischemia. These changes were cancelled by preischemic inhibition of PKA but not PKC. Furthermore, either Rho-kinase inhibition (hydroxyfasudil or Y27632) or actin cytoskeletal deactivation (cytochalasin-D) during sustained ischemia achieved the same infarct limitation as preischemic PKA activation without affecting systemic hemodynamic parameters, the area at risk, or collateral blood flow. Conclusions— Transient preischemic activation of PKA reduces infarct size through Rho-kinase inhibition and actin cytoskeletal deactivation during sustained ischemia, implicating a novel mechanism for cardioprotection by ischemic preconditioning independent of PKC and a potential new therapeutic target.

Background—Carvedilol is a β-adrenoceptor blocker with a vasodilatory action that is more effective for the treatment of congestive heart failure than other β-blockers. Recently, carvedilol has been reported to reduce oxidative stress, which may consequently reduce the deactivation of adenosine-producing enzymes and increase cardiac adenosine levels. Therefore, carvedilol may also have a protective effect on ischemia and reperfusion injury, because adenosine mediates cardioprotection in ischemic hearts.Methods and Results—In anesthetized dogs, the left anterior descending coronary artery was occluded for 90 minutes, followed by reperfusion for 6 hours. Carvedilol reduced the infarct size (15.0±2.8% versus 40.9±4.2% in controls), and this effect was completely reversed by the nonselective adenosine receptor antagonist 8-sulfophenyltheophylline (45.2±5.4%) or by an inhibitor of ecto-5′-nucleotidase (44.4±3.6%). There were no differences of either area at risk or collateral flow among the various groups. When the coronary perfusion pressure was reduced in other dogs so that coronary blood flow was decreased to 50% of the nonischemic level, carvedilol increased coronary blood flow (49.4±5.6 to 73.5±7.5 mL · 100 g−1· min−1;PPConclusions—Carvedilol shows a cardioprotective effect against ischemia and/or reperfusion injury via adenosine-dependent mechanisms.

Background— Some studies have shown that metformin activates AMP-activated protein kinase (AMPK) and has a potent cardioprotective effect against ischemia/reperfusion injury. Because AMPK also is activated in animal models of heart failure, we investigated whether metformin decreases cardiomyocyte apoptosis and attenuates the progression of heart failure in dogs. Methods and Results— Treatment with metformin (10 μmol/L) protected cultured cardiomyocytes from cell death during exposure to H 2 O 2 (50 μmol/L) via AMPK activation, as shown by the MTT assay, terminal deoxynucleotidyl transferase–mediated dUTP nick-end labeling staining, and flow cytometry. Continuous rapid ventricular pacing (230 bpm for 4 weeks) caused typical heart failure in dogs. Both left ventricular fractional shortening and left ventricular end-diastolic pressure were significantly improved in dogs treated with oral metformin at 100 mg · kg −1 · d −1 (n=8) (18.6±1.8% and 11.8±1.1 mm Hg, respectively) compared with dogs receiving vehicle (n=8) (9.6±0.7% and 22±0.9 mm Hg, respectively). Metformin also promoted phosphorylation of both AMPK and endothelial nitric oxide synthase, increased plasma nitric oxide levels, and improved insulin resistance. As a result of these effects, metformin decreased apoptosis and improved cardiac function in failing canine hearts. Interestingly, another AMPK activator (AICAR) had effects equivalent to those of metformin, suggesting the primary role of AMPK activation in reducing apoptosis and preventing heart failure. Conclusions— Metformin attenuated oxidative stress–induced cardiomyocyte apoptosis and prevented the progression of heart failure in dogs, along with activation of AMPK. Therefore, metformin may be a potential new therapy for heart failure.

Background — Phosphodiesterase III inhibitors (PDEIII-Is) improve the hemodynamic status of heart failure via inotropic/vasodilatory effects attributable to the increase in intracellular cAMP level. Direct cardioprotection by PDEIII-Is and its underlying mechanisms, however, have not been identified. We tested the infarct size–limiting effect of PDEIII-Is and the roles of cAMP, protein kinase (PK) A, PKC, and mitogen-activated protein kinase (MAPK) families in open-chest dogs. Methods and Results — Milrinone, olprinone (PDEIII-Is), or dibutyryl-cAMP (db-cAMP) was injected intravenously 30 minutes before 90-minute ischemia, followed by 6 hours of reperfusion. Olprinone was also examined with an intracoronary cotreatment with a PKA inhibitor (H89), a PKC inhibitor (GF109203X), an extracellular signal–regulated kinase kinase (MEK) inhibitor (PD98059), or a p38 MAPK inhibitor (SB203580) throughout the preischemic period. Either PDEIII-Is or db-cAMP caused substantial hemodynamic changes, which returned to control levels in 30 minutes. Collateral flow and percent risk area were identical for all groups. Both PDEIII-Is and db-cAMP increased myocardial p38 MAPK activity during the preischemic period, which was blocked by H89, but not by GF109203X. Both PDEIII-Is and db-cAMP reduced infarct size (19.1±4.1%, 17.5±3.3%, and 20.3±4.8%, respectively, versus 36.1±6.2% control, P Conclusions — Pretreatment with PDEIII-Is has cardioprotective effects via cAMP-, PKA-, and p38 MAPK–dependent but PKC-independent mechanisms in canine hearts.